Above Ground Pool Gallons Calculator

This calculator works out the water volume of an above-ground pool in US gallons. You enter the pool’s shape, dimensions, and average water depth, and it returns the total gallons needed to fill it. The result is based on the standard geometric volume formula adjusted for the pool’s shape.

Formula

The calculator uses the geometric volume of the pool’s shape, then converts cubic feet to gallons. For a round pool: Gallons = Ï€ × (diameter/2)² × depth × 7.48. For a rectangular or oval pool: Gallons = length × width × depth × 7.48 (for oval, multiply by 0.8 to account for the rounded corners). The factor 7.48 converts cubic feet to US gallons (1 cubic foot = 7.48 gallons). Variables: diameter (ft), length (ft), width (ft), depth (ft) – all measured in feet.

Worked Example

Using the default values: a round pool with diameter 24 ft and average depth 4 ft.

1. Radius = 24 / 2 = 12 ft
2. Area = π × 12² = 3.14159 × 144 = 452.39 sq ft
3. Volume = 452.39 × 4 = 1809.56 cubic ft
4. Gallons = 1809.56 × 7.48 = 13,535 gallons

The calculator rounds to 13,535 gallons.

Why Pool Volume Matters

Knowing your pool’s gallon capacity is essential for three main reasons: chemical dosing (chlorine, pH adjusters, algaecides), sizing the pump and filter, and estimating water fill time and cost. Most chemical products list dosages per 10,000 gallons, so an accurate volume prevents under- or over-dosing. An undersized pump can’t circulate the water effectively, leading to algae and cloudy water.

How to Measure Your Pool Correctly

Measure the water depth, not the pool wall height. The water level is typically 6–12 inches below the top of the wall. For an above-ground pool, the depth is usually fairly uniform, but if you have a deep end, measure at several points and average them. For round pools, measure the diameter across the widest point, from outside edge to outside edge. For oval pools, measure the longest and widest points. Always measure in feet for this calculator.

Common Mistakes and Misconceptions

• Using wall height instead of water depth – this overestimates volume by up to 20%.
• Mixing units – if you measure in inches, convert to feet (divide by 12) before entering.
• Forgetting the 0.8 oval factor – an oval pool is not a perfect rectangle; the rounded ends reduce volume by about 20%.
• Assuming all gallons are the same – this calculator gives US gallons. Imperial gallons are about 20% larger (1 imperial gallon = 1.2 US gallons).

Limitations of the Formula

The formula assumes a perfectly flat bottom and vertical walls, which is true for most above-ground pools. However, some pools have a slight slope or a deeper center. The average depth method works well for these, but for extreme slopes, you might need to calculate the volume in sections. Also, the formula does not account for water displaced by ladders, people, or pool toys – for chemical dosing, that’s negligible.

Frequently Asked Questions

How many gallons is a 24-foot round pool with 4-foot walls?

If the water depth is 4 feet, the calculator gives 13,535 gallons. But if the water is only 3.5 feet deep (typical), the volume is about 11,843 gallons. Always use the actual water depth.

How do I convert from liters to gallons?

1 US gallon = 3.785 liters. So divide the liters by 3.785 to get US gallons. For example, 10,000 liters ÷ 3.785 = 2,642 gallons.

Why does my pool store say a different number?

Pool stores often use the pool’s maximum capacity (wall height) rather than actual water depth. They may also round the diameter to the nearest foot. The difference can be 10–15%, which is significant for chemical dosing.

Can I use this calculator for an oval pool?

Yes, select the oval shape and enter the length and width. The calculator multiplies by 0.8 to approximate the rounded ends. For a more precise oval, you could use the formula for an ellipse (π × (l/2) × (w/2) × depth × 7.48), but the 0.8 factor is a common and accurate approximation.

How long will it take to fill my pool with a garden hose?

A typical garden hose flows at 5–10 gallons per minute. For a 13,535-gallon pool, that’s 22–45 hours. Check your local water pressure and hose diameter for a better estimate.

What if my pool has a deep end?

Measure the depth at the shallow end and the deep end, then average them. Use that average in the calculator. For a more accurate result, split the pool into two sections (shallow and deep) and calculate each separately, then add them.

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in t | Shape | Round=1, Oval=0.8, Rectangular=1 | 1
in d | Diameter (ft) | ft | 24 | 0
in l | Length (ft) | ft | 0 | 0
in w | Width (ft) | ft | 0 | 0
in h | Average Depth (ft) | ft | 4 | 0
out gallons | Estimated Gallons | gal | (t == 1 ? (3.14159 * (d/2)^2 * h * 7.48) : (t == 0.8 ? (l * w * h * 7.48) : (l * w * h * 7.48))) | 0